U.S. Pat. No. 5,820,514 discloses a belt-type continuously variable transmission (hereinafter referred to as belt CVT) for use in a vehicle.
The belt CVT comprises a primary pulley for inputting the drive force of an engine, a secondary pulley for outputting the drive force to a drive wheel, and a V-belt that is wrapped around the primary pulley and secondary pulley. In the primary pulley and secondary pulley, pulley grooves for accepting the belt are each varied in width by oil pressure. Changes in the width of the pulley grooves change the contact radius between the V-belt and the pulley, which results in changing the rotation speed ratio of the primary pulley and the secondary pulley, or in other words the speed ratio of the transmission.
The output rotation of the engine is transmitted to the primary pulley via a torque converter and a forward/reverse change-over mechanism.
The forward/reverse change-over mechanism comprises a forward clutch that is engaged during forward travel of the vehicle, or in other words when the driver places a shift lever in a drive range (D), and a reverse clutch that is engaged during reverse travel, or in other words when the driver places the shift lever in the reverse range (R). When the shift lever is in the neutral range (N), both of these clutches are released, and the output rotation of the engine is not transmitted to the primary pulley. These clutches are engaged by means of oil pressure, and the clutches are released from an engaged state by the release of oil pressure into a drain.